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    SubjectRe: [RFC v5 06/11] [media] vb2: add explicit fence user API
    Em Fri, 17 Nov 2017 14:29:23 +0100
    Hans Verkuil <hverkuil@xs4all.nl> escreveu:

    > On 15/11/17 18:10, Gustavo Padovan wrote:
    > > From: Gustavo Padovan <gustavo.padovan@collabora.com>
    > >
    > > Turn the reserved2 field into fence_fd that we will use to send
    > > an in-fence to the kernel and return an out-fence from the kernel to
    > > userspace.
    > >
    > > Two new flags were added, V4L2_BUF_FLAG_IN_FENCE, that should be used
    > > when sending a fence to the kernel to be waited on, and
    > > V4L2_BUF_FLAG_OUT_FENCE, to ask the kernel to give back an out-fence.
    > >
    > > v4:
    > > - make it a union with reserved2 and fence_fd (Hans Verkuil)
    > >
    > > v3:
    > > - make the out_fence refer to the current buffer (Hans Verkuil)
    > >
    > > v2: add documentation
    > >
    > > Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.com>
    > > ---
    > > Documentation/media/uapi/v4l/buffer.rst | 15 +++++++++++++++
    > > drivers/media/usb/cpia2/cpia2_v4l.c | 2 +-
    > > drivers/media/v4l2-core/v4l2-compat-ioctl32.c | 4 ++--
    > > drivers/media/v4l2-core/videobuf2-v4l2.c | 2 +-
    > > include/uapi/linux/videodev2.h | 7 ++++++-
    > > 5 files changed, 25 insertions(+), 5 deletions(-)
    > >
    > > diff --git a/Documentation/media/uapi/v4l/buffer.rst b/Documentation/media/uapi/v4l/buffer.rst
    > > index ae6ee73f151c..eeefbd2547e7 100644
    > > --- a/Documentation/media/uapi/v4l/buffer.rst
    > > +++ b/Documentation/media/uapi/v4l/buffer.rst
    > > @@ -648,6 +648,21 @@ Buffer Flags
    > > - Start Of Exposure. The buffer timestamp has been taken when the
    > > exposure of the frame has begun. This is only valid for the
    > > ``V4L2_BUF_TYPE_VIDEO_CAPTURE`` buffer type.
    > > + * .. _`V4L2-BUF-FLAG-IN-FENCE`:
    > > +
    > > + - ``V4L2_BUF_FLAG_IN_FENCE``
    > > + - 0x00200000
    > > + - Ask V4L2 to wait on fence passed in ``fence_fd`` field. The buffer
    > > + won't be queued to the driver until the fence signals.
    > > +
    > > + * .. _`V4L2-BUF-FLAG-OUT-FENCE`:
    > > +
    > > + - ``V4L2_BUF_FLAG_OUT_FENCE``
    > > + - 0x00400000
    > > + - Request a fence to be attached to the buffer. The ``fence_fd``
    > > + field on
    > > + :ref:`VIDIOC_QBUF` is used as a return argument to send the out-fence
    > > + fd to userspace.
    >
    > How would userspace know if fences are not supported? E.g. any driver that does
    > not use vb2 will have no support for it.
    >
    > While the driver could clear the flag on return, the problem is that it is a bit
    > late for applications to discover lack of fence support.
    >
    > Perhaps we do need a capability flag for this? I wonder what others think.

    We're almost running out of flags at v4l2 caps (and at struct v4l2_buffer).

    So, I would prefer to not add more flags on those structs if there is
    another way.

    As the fences out of order flags should go to ENUM_FMT (and, currently
    there's just one flag defined there), I wander if it would make sense
    to also add CAN_IN_FENCES/CAN_OUT_FENCES flags there, as maybe we
    would want to disable/enable fences based on the format.

    >
    > Regards,
    >
    > Hans
    >
    > >
    > >
    > >
    > > diff --git a/drivers/media/usb/cpia2/cpia2_v4l.c b/drivers/media/usb/cpia2/cpia2_v4l.c
    > > index 3dedd83f0b19..6cde686bf44c 100644
    > > --- a/drivers/media/usb/cpia2/cpia2_v4l.c
    > > +++ b/drivers/media/usb/cpia2/cpia2_v4l.c
    > > @@ -948,7 +948,7 @@ static int cpia2_dqbuf(struct file *file, void *fh, struct v4l2_buffer *buf)
    > > buf->sequence = cam->buffers[buf->index].seq;
    > > buf->m.offset = cam->buffers[buf->index].data - cam->frame_buffer;
    > > buf->length = cam->frame_size;
    > > - buf->reserved2 = 0;
    > > + buf->fence_fd = -1;
    > > buf->reserved = 0;
    > > memset(&buf->timecode, 0, sizeof(buf->timecode));
    > >
    > > diff --git a/drivers/media/v4l2-core/v4l2-compat-ioctl32.c b/drivers/media/v4l2-core/v4l2-compat-ioctl32.c
    > > index 821f2aa299ae..3a31d318df2a 100644
    > > --- a/drivers/media/v4l2-core/v4l2-compat-ioctl32.c
    > > +++ b/drivers/media/v4l2-core/v4l2-compat-ioctl32.c
    > > @@ -370,7 +370,7 @@ struct v4l2_buffer32 {
    > > __s32 fd;
    > > } m;
    > > __u32 length;
    > > - __u32 reserved2;
    > > + __s32 fence_fd;
    > > __u32 reserved;
    > > };
    > >
    > > @@ -533,7 +533,7 @@ static int put_v4l2_buffer32(struct v4l2_buffer *kp, struct v4l2_buffer32 __user
    > > put_user(kp->timestamp.tv_usec, &up->timestamp.tv_usec) ||
    > > copy_to_user(&up->timecode, &kp->timecode, sizeof(struct v4l2_timecode)) ||
    > > put_user(kp->sequence, &up->sequence) ||
    > > - put_user(kp->reserved2, &up->reserved2) ||
    > > + put_user(kp->fence_fd, &up->fence_fd) ||
    > > put_user(kp->reserved, &up->reserved) ||
    > > put_user(kp->length, &up->length))
    > > return -EFAULT;
    > > diff --git a/drivers/media/v4l2-core/videobuf2-v4l2.c b/drivers/media/v4l2-core/videobuf2-v4l2.c
    > > index 0c0669976bdc..110fb45fef6f 100644
    > > --- a/drivers/media/v4l2-core/videobuf2-v4l2.c
    > > +++ b/drivers/media/v4l2-core/videobuf2-v4l2.c
    > > @@ -203,7 +203,7 @@ static void __fill_v4l2_buffer(struct vb2_buffer *vb, void *pb)
    > > b->timestamp = ns_to_timeval(vb->timestamp);
    > > b->timecode = vbuf->timecode;
    > > b->sequence = vbuf->sequence;
    > > - b->reserved2 = 0;
    > > + b->fence_fd = -1;
    > > b->reserved = 0;
    > >
    > > if (q->is_multiplanar) {
    > > diff --git a/include/uapi/linux/videodev2.h b/include/uapi/linux/videodev2.h
    > > index cd6fc1387f47..311c3a331eda 100644
    > > --- a/include/uapi/linux/videodev2.h
    > > +++ b/include/uapi/linux/videodev2.h
    > > @@ -925,7 +925,10 @@ struct v4l2_buffer {
    > > __s32 fd;
    > > } m;
    > > __u32 length;
    > > - __u32 reserved2;
    > > + union {
    > > + __s32 fence_fd;
    > > + __u32 reserved2;
    > > + };
    > > __u32 reserved;
    > > };
    > >
    > > @@ -962,6 +965,8 @@ struct v4l2_buffer {
    > > #define V4L2_BUF_FLAG_TSTAMP_SRC_SOE 0x00010000
    > > /* mem2mem encoder/decoder */
    > > #define V4L2_BUF_FLAG_LAST 0x00100000
    > > +#define V4L2_BUF_FLAG_IN_FENCE 0x00200000
    > > +#define V4L2_BUF_FLAG_OUT_FENCE 0x00400000
    > >
    > > /**
    > > * struct v4l2_exportbuffer - export of video buffer as DMABUF file descriptor
    > >
    >


    --
    Thanks,
    Mauro

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